Aspergillus species are believed to be cosmopolitan organisms, existing as unstructured global populations. Species belonging to this taxon, including A. fumigatus, A. terreus, A. flavus and others, cause invasive aspergillosis (IA) predominantly in severely immunocompromised individuals. The majority of studies with A. fumigatus have demonstrated no association between genotypes and geography. Several studies employing comparative sequence analysis of different loci, including protein coding, intergenic and microsatellite containing regions, arrived at the conclusion that there was no correlation between genotype and geographical origin among A. fumigatus isolates [1–3]. In contrast to these observations, one study demonstrated the presence of multiple, well-supported phylogenetic clusters amongst A. fumigatus isolates from a collection of isolates geographically dispersed across North America . The locus sequenced was a single gene encoding a putative cell surface protein, Afu3g08990 (CSP), in which polymorphisms consisted of insertions and deletions within a repeat region. The authors speculated that the presence of clusters may have been undetected previously due to the reliance on data from loci lacking sufficient polymorphisms.
Aspergillus terreus is the second or third most common etiological agent of IA and interestingly, appears to be the most common cause of infection in some medical centers, suggesting ecological specificity for this organism [5–7]. Previous efforts to determine population structure in A. terreus have been hampered by the lack of reliable methods for exploiting genetic variability to distinguish or group isolates. Balajee et al., employing a multi-gene sequencing approach to a large global collection of isolates previously identified as A. terreus, showed that no evidence of endemism existed but were able to define a genotypically distinct species, A. alabamensis . The use of multi-locus comparative sequence analysis to explore population structure in A. terreus supported the existence of a single globally distributed population . On the other hand, multiple studies using molecular fingerprinting methods, including RAPD, demonstrated high genotypic diversity among A. terreus isolates [9, 10], with no evidence of endemism [9, 11]. Thus, even as new species are defined within groups of isolates identified as A. terreus, support for the idea that A. terreus exists as a single, genotypically diverse, global population, lacking phylogeographic structure, continues [8–10].
A recent study investigating amphotericin B (AMB) susceptibility of a worldwide A. terreus collection found that isolates recovered from different parts of the world had different patterns of AMB susceptibility . At that time, no attempt was made to study the association between genotypic relatedness and antifungal susceptibility in this set of isolates. In the present investigation, this A. terreus isolate collection was genotyped employing the highly discriminatory genome-wide DNA fingerprinting method, Inter-Simple Sequence Repeat (ISSR) PCR  to (a) assess the use of this fingerprinting method for discriminatory genotyping of A. terreus; (b) evaluate the association between AMB susceptibility and genotype in this global collection of isolates; and (c) attempt to map geography onto genotypically related clusters of isolates. Results of this study revealed the possible global sub-structuring of genotypes and the presence of the recently described cryptic species A. alabamensis in Italy.